Indicating device



`Aug. 30, 1,932. F. SLEBER INDICATING DEVICE Fild Sept. 4, 1929 FR/rS/EEER Hrm/mfr I wire is placed is increased,

'thereacross which,

age in the wire or meters of the usual size.

:rent for the wire is Patented Aug. 30, 1932 UNITED STA FRITZ SIEBER, OFBADEN, SWITZERLAND INDICATING DEVICE Application sied september 4, 1929,serial No. 390,225,

rlhis invention relates to improvements in devices for measuring thepressure of gases and, particularly, te manometers which operate independence on the rate of heat transfer from a heated wire to a gassurrounding the wire, the pressure of which gas is to be measured. y f

lt is `well known that the rate of heat transference from a wire freelysupported in a surrounding atmosphere or other surrounding gas is afunction of the vapor density and that only a negligible quantity ofheat flows by conduction-along the wire itself. lf the vapor density ofthe gas :in which the not vthe rate of heat dissipation from the wire tothe gas will be increased and the resistance ofthe wire to the flow ofelectric .current will be decreased and vice versa. If a Wire is,accordingly, electrically heated by means of a constant current, theamount of IR drop of course, depends on the resistance of the wire; maybe utilized a measurement of the vapor density of the gas in which thewire is located.

rlhe gas pressure surrounding` the hot wire of such'manomete'rs mayaccordingly be read by the use of electrical measuring devices, such asvoltmeters which measure the voltthe voltage differences between severalwires as a function of the pressure. The total load of such electricalmeasuring device is, however, very small, it being of the order of onemilliwatt for mano- A rotating coil direct current electrical measuringinstru-A ment for such small load may be'easily con structed in aconvenient size' but it is piacically impossible to construct rotatingcoil alternating current direct reading instruments for fractions of avolt, for the reason that the load necessary for such instruments is atleast one watt. Y f

It is, therefore, among the objects of the present invention to providea manometer of the hot wire type in which the heating curtaken from asource of alternating current and the indications' are read on a gaugecalibrated to indicate the pressure directly.

and in Germany September 14, 1928.

' 'Another object of the invention is to provide a hot wire manometer inwhich alternat-V ing current supplies the manometer in such manner thatthe alternating current is used to lmeasure the pressure Without thenecessity of supplyingadditional energy thereto.

Objects and advantages, above set forth, will be apparent followingdescription, and the Vdrawing in other than those from the which Figure1v shows an embodiment of the present invention in which an alternatingcurrent measuring instrument is utilized to indicate the degree ofvacuum present in the chamber whereof the vapor density is to bedetermined.

Fig. 2 showslaniodified embodiment of the present invention in which themeasuring device is supplied with alternating current and the pressureindications are read on a direct current measuring' instrument.

Referring more particularly by characters of reference,

als 4,

windings respectively of operates with a saturated core and 6, 9indicate the primary and secondary windings re'- speetively of a withthe drawing, the primary to the drawing reference numer- 8 indicate theprimary and secondary a transformer which transformer which operates acore having an air gap. As shown in windings 4, 6 are serially connectedin circuit with a resistance 7 to line 3L The secondary windings 8, 9are,

however, connected in opposition to each other stant to thereby supplysubstantially a concurrent to the Wheatstone bridge arms,

hereinafter described, during periods of rise and fall of potentialofline 3 within wide limits. l y

The current fromv the secondaries 8, 9 of the combined transformersis'supplied to diagonally opposed points of a plurality of resistancewires pairs Wheatstone bridge.

arms

11, 12, 13 and 14 arranged in form of a normally balanced Two of thewires or 11, 12 of the bridge are enclosed within (as indicated by thedotdensity of the in the gas is to be measured and the other two arms l13,14 of the bridge are suppcrted in the atmosphere.

yThe primary winding 16. of a d transformer is connected with lthe il Ulli

the arms equally. Because of the fact that" arms 11, 12 are, however,enclosed withina space wherein the density of the gases is dif-,ferentfrom .that surrounding the arms 13, 14,

l the rate of heat dissipation from the arms 13,

14 is in direct relation tothe difference between the vapor densityofthe. gasesv sur;

rounding the two pairs of arms. It is accordingly possible-to calibratethe alternating current measuring instrument 18 in such-manner that thevapor density surrounding the arms 11, 12 may be read directlytherefrom.

Instead of utilizing the second transformer 1G, 17, an electric currentrectifying device 19 may be connected in the conductors leading from theVVheatstone bridge arrangement of the resistance arms which .conductorswill then include a direct current measuring inlstrument 21. Theelectric currentrectifying device may be of any suitable construction,such as an oXide coated plate rectifier or a hot cathode tube as may bedesired.

It will be apparent from. the above description of the construction andoperation of a [hot wire pressure measuring device or manometer, thatelectrical measuring instruments having the smallest known energyrequirements Vmay be utilized as indicators in such manner that theprimary load require- /ment is only a very small fraction of the amountnecessary for theuse of a load indicator. The alternating currentmeasuring instrument 18 is suitably formed as Aan electro-static.voltmeter. The energy requirements of such electro-static voltmeters isso small that only about 1/100 watt transformer losses need to beconsidered.V Y Y Although but two embodiments of this invention havebeen illustrated anddescribed,v

' it will be understood that various other embodiments are possible, and:that various changes may be made without departing from the spirit ofthe claims. A

The invention as claimed is: 1'. In a system for measuring andindicating gas pressures, the combination comprisinvention or the scopeof the ing, a source of 'alternatingv current supply, ,a plurality ofelectrical resistance VKranged and connected as a four armed closed'elements ar- VVVheatstone bridge, two oppositely disposed `o nly ofsaidfarms being arranged within the gas 4to be measured, seriallyconnected transformers interconnecting said current supply and saidelements at opposite nodal points of said bridge to eff-ect the flow ofa substantially constant current through said secondary windings andsaid elements, and indicating means connected with said bridge at theother opposite nodal points thereof and actuated responsively to thesaid supply current in dependence on the transfer of heat from saidresistance elements resulting from flow of Y ysaid current' therethroughto the gas to be measuredto indicate the pressure thereof.

2. Ina system for measuring and indicating gas pressures, thecombinationcompris- 1ng,`a source Aof alternating current; "supply, a plurality oftransformers, a primary winding and a secondary winding for each of saidtransformers, a current limiting resistance, said primary *beingVserially connected with said current supply, a plurality of Y electrical.resistance elements arranged and connected as a four armed closedNheatstone bridge, two oppositely disposed only of said arms beingarranged within the gas to be measured, said secondary windingsconnected to said Wheatstone bridgel at oppositefnodal points thereof toeffectV a llow of substantially-constant current through saidsecondarywindingsand said resistanceelements, and a measuring instrumentVconnected,V to Vthe other opposite nodal points ofsaid bridge actuatedresponsively to said supply current in dependence on the density of thegas to bemeasured to indicate thepressure thereof. 3; In a system formeasuring and indicating gas pressures, the combinationV comprising, asource of alternating current supply, a plurality of transformers eachincluding' a primary winding and a secondary winding, an electricalresistance, said resistance and` said primary windings being seriallyconnected withsaid current supply, a plurality of resistance elementsarranged and connected as a four armed closed Wheatstone bridge, twooppositely disposed only of said `elements being arranged inthe gas tobe measured, the said secondary windings being/connected to the saidbridge at opposite nodal. points rthereof to effect flow ofsubstantially constant .current through said secondary windingsand saidbridge, `a direct current measuring in- Y strument and an electric valveserially connected with the said bridge at the other opposite nodalpointsthereof the said instrument ,being actuated responsively to thesaid supply current in dependence on the density of the gas to be measued to Vindicate the pressurethereof. u

In testimony whereof I have hereuntosubscribedmy name this 13th day.l ofAugust," A. D. 1929. v i, Y f d FRITZ SIEBER;y

Vwindings and said resistanceAV

